1) Field of the Invention
The present invention relates to a variable magnification lens, specifically to a small-sized, wide-angle variable magnification lens and a camera using the same.
2) Description of Related Art
A variable magnification lens of two-unit configuration that includes, in order from the object side, a positive front unit and a negative rear unit has often been used because of its simple structure. Also, in recent years, a requirement has grown to give a variable magnification lens for a compact camera a much smaller size and higher magnification ratio. In particular, a requirement for a wider field angle at the short-focal-length end in magnification change has grown. In addition, a further size reduction and cost reduction are required. For example, each of Japanese Patent Application Preliminary Publication (KOKAI) No. Sho 57-201213, Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 2-6917, Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 3-185412, Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 10-96858, Japanese Patent Application Preliminary Publication (KOKAI) No. 2000-305015 and U.S. Pat. No. 5,493,448 proposes an inexpensive optical system composed of five or so lens elements in the entire system. Also, each of Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 6-82696, Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 6-160713, Japanese Patent Application Preliminary Publication (KOKAI) No. Hei 11-305123, Japanese Patent Application Preliminary Publication (KOKAI) No. 2001-194588, U.S. Pat. No. 5,270,867, and U.S. Pat. No. 5,900,991 proposes an optical system having a field angle wider than 70 degrees at the wide-angle end. Further, each of Japanese Patent Application Preliminary Publication (KOKAI) No. 2000-137163, Japanese Patent Application Preliminary Publication (KOKAI) No. 2001-116995, and U.S. Pat. No. 4,936,661 proposes a wide field-angle, high magnification-ratio optical system having a small number of components.
While each of above-cited JP KOKAI No. Sho 57-201213, JP KOKAI No. Hei 2-6917, JP KOKAI No. Hei 3-185412, JP KOKAI No. Hei 10-96858, JP KOKAI No. 2000-305015, and U.S. Pat. No. 5,493,448 proposes an optical system composed of five or so lens elements, such an optical system has a field angle narrower than 70 degrees and a variable magnification ratio smaller than 2.2. Also, according to each of JP KOKAI No. Hei 6-82696, JP KOKAI No. Hei 6-160713, JP KOKAI No. Hei 11-305123, JP KOKAI No. 2001-194588, U.S. Pat. No. 5,270,867, and U.S. Pat. No. 5,900,991, while the optical system achieves a wide field angle of 70 degrees or greater at the wide-angle end, its telephoto ratio at the telephoto end is as small as 1. In contrast, according to each of JP KOKAI No. 2000-137163, JP KOKAI No. 2001-116995, and the third and fourth embodiments of U.S. Pat. No. 4,936,661, the optical system achieves a wide field angle of 70 degrees or greater at the wide-angle end and a variable magnification ratio greater than 2.5 while keeping a telephoto ratio smaller than 0.96, and thus can be regarded as achieving a wide field angle, a high magnification ratio and a small size. However, in each of JP KOKAI No. 2000-137163, JP KOKAI No. 2001-116995 and the third and fourth embodiments of U.S. Pat. No. 4,936,661, the optical system is composed of six or more lens elements. In addition, according to U.S. Pat. No. 4,936,661, aspherical surfaces are applied to three lens elements.
According to the first aspect of the present invention, a variable magnification lens includes, in order from an object side, a first lens unit (front unit) having a positive refracting power and a second lens unit (rear unit) having a negative refracting power, a magnification change being performed by a change of a distance between the first lens unit and the second lens unit. In the variable magnification lens, the first lens unit consists of, in order from the object side, a sub-unit 1a that includes at least one lens element, an aperture stop, and a sub-unit 1b that includes at least one lens element, and all lens elements constituting the first lens unit are arranged with intervening air spaces between one another. The variable magnification lens satisfies the following conditions (1) and (2):
1.1 less than FLw/IH less than 1.35xe2x80x83xe2x80x83(1) 
0.80 less than TLt/FLt less than 0.94xe2x80x83xe2x80x83(2) 
where FLw is a focal length in a wide-angle end position, FLt is a focal length in a telephoto end position, IH is a maximum image height, and TLt is a distance, in the telephoto end position, from a first surface to an image surface.
Also, according to the second aspect of the present invention, a variable magnification lens includes, in order from an object side, a first lens unit (front unit) having a positive refracting power and a second lens unit (rear unit) having a negative refracting power, a magnification change being performed by a change of a distance between the first lens unit and the second lens unit. In the variable magnification lens, the first lens unit consists of, in order from the object side, a sub-unit 1a that includes at least one lens element, an aperture stop, and a sub-unit 1b that includes at least one lens element, and all lens elements constituting the first lens unit are arranged with intervening air spaces between one another. The variable magnification lens satisfies the following conditions (1) and (3):
1.1 less than FLw/IH less than 1.35xe2x80x83xe2x80x83(1) 
2.50 less than FLt/FLw less than 5.0xe2x80x83xe2x80x83(3) 
where FLw is a focal length in a wide-angle end position, FLt is a focal length in a telephoto end position, and IH is a maximum image height.
Also, according to the third aspect of the present invention, a variable magnification lens includes, in order from an object side, a first lens unit (front unit) having a positive refracting power and a second lens unit (rear unit) having a negative refracting power, a magnification change being performed by a change of a distance between the first lens unit and the second lens unit. In the variable magnification lens, the first lens unit consists essentially of a lens element having a negative refracting power and two lens elements having positive refracting powers, all the lens elements constituting the first lens unit being arranged with intervening air spaces between one another. The variable magnification lens satisfies the following conditions (1), (3), (4) and (5):
1.1 less than FLw/IH less than 1.35xe2x80x83xe2x80x83(1) 
2.50 less than FLt/FLw less than 5.0xe2x80x83xe2x80x83(3) 
0.2 less than Fbw/FLw less than 0.37xe2x80x83xe2x80x83(4) 
0.4 less than FL1G/FLw less than 0.7xe2x80x83xe2x80x83(5) 
where FLw is a focal length in a wide-angle end position, FLt is a focal length in a telephoto end position, IH is a maximum image height, Fbw is a paraxial amount of a back focal distance in the wide-angle end position, and FL1G is a focal length of the first lens unit.
Also, a camera according to the present invention includes any one of the variable magnification lenses set forth above, a field stop that regulates the maximum image height IH formed by the variable magnification lens, and an optical finder that is configured separate from the variable magnification lens.
These and other features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.